Despite stepped-up military assistance to Iraq to fight Islamic State militants, and President Obama’s public commitment to keeping Iraq unified, Iraqis have long suspected a nefarious plot by the Americans to break up their country.

Their suspicions are intensified by a century of painful experience with Western intervention, much of it recent, and are embellished by a cultural fascination with conspiracies of all stripes. So when news came out this week that congressional Republicans were proposing to directly arm Iraqi Sunnis and Kurds without the involvement of the Shiite-led central government, it was immediately and widely taken as proof that the American plot against Iraq had entered a new phase.

The front page of one Iraqi newspaper on Thursday showed a map of the country, wrapped in a chain to symbolize the grip of the United States and divided into three nations: Shiastan, Sunnistan and Kurdistan. A headline in red declared, “Congress proposes to deal with Kurds and Sunnis as two states.” […]